1. Field of the Invention
The present invention relates to a substrate processing apparatus and a substrate processing method for processing a substrate. Examples of the substrate to be processed include semiconductor wafers, glass substrates for liquid crystal display devices, glass substrates for plasma display devices, substrates for optical disks, substrates for magnetic disks, substrates for magneto-optical disks, and substrates for photo masks.
2. Description of Related Art
In production processes for semiconductor devices and liquid crystal display devices, a single substrate processing apparatuses is used for processing a surface of a substrate a semiconductor wafer, a glass substrate for a liquid crystal display panel or the like with a process liquid. For reduction of the consumption of the process liquid, some of the substrate processing apparatuses of this type are adapted to recover the process liquid used for the process of the substrate and reuse the recovered process liquid for the subsequent process.
Such a substrate processing apparatus adapted to reuse the process liquid includes, for example, a spin chuck which horizontally holds and rotates a substrate, a bottomed hollow cylindrical cup in which the spin chuck is accommodated, and a splash guard provided vertically movably with respect to the cup.
The cup has an annular drain channel provided around the spin chuck. The cup further has three annular recovery channels triply concentrically provided around the drain channel. The drain channel is connected to a waste liquid drain for draining the process liquid. The recovery channels are each connected to a recovery drain for guiding the process liquid to a recovery tank.
The splash guard includes four guards vertically and radially overlapped with each other. The guards each have a substantially rotationally symmetrical shape about the rotation axis of the substrate. Upper edge portions of the guards are each inclined upward toward the rotation axis of the substrate. Upper edges of the guards are located in predetermined spaced relation on a cylindrical plane having a center axis aligning with the rotation axis of the substrate. The guards are respectively associated with the recovery channels and the drain channel, and lower edges of the guards are respectively inserted in the recovery channels and the drain channel. That is, the uppermost guard (first guard) is associated with the outermost recovery channel (first channel), and the lower edge of the first guard is inserted in the first recovery channel. A guard (second guard) immediately below the first guard is associated with a recovery channel (second channel) disposed inwardly adjacent to the first recovery channel, and the lower edge of the second guard is inserted in the second recovery channel. A guard (third guard) immediately below the second guard is associated with the innermost recovery channel (third recovery channel inwardly adjacent to the second recovery channel), and the lower edge of the third guard is inserted in the third recovery channel. The lowermost guard (fourth guard) is associated with the drain channel, and the lower edge of the fourth guard is inserted in the drain channel.
A first recovery port is defined between the upper edge of the first guard and the upper edge of the second guard for introducing the process liquid scattered from the substrate into the first recovery channel. A second recovery port is defined between the upper edge of the second guard and the upper edge of the third guard for introducing the process liquid scattered from the substrate into the second recovery channel. A third recovery port is defined between the upper edge of the third guard and the upper edge of the fourth guard for introducing the process liquid scattered from the substrate into the third recovery channel. A drain port is defined between the fourth guard and a bottom surface of the cup for introducing the process liquid scattered from the substrate into the drain channel.
A lift driving mechanism, for example, including a ball screw mechanism and the like is connected to the splash guard. The four guards are moved up and down together by the lift driving mechanism.
In the substrate processing apparatus having the aforesaid construction, plural types of process liquids are sequentially supplied to the surface of the substrate to treat the substrate surface sequentially with the plural types of process liquids. Further, the plural types of process liquids used for the processes are separately recovered.
More specifically, the substrate surface is processed with a first process liquid by supplying the first process liquid to the substrate surface while rotating the substrate by the spin chuck. The first process liquid supplied to the substrate surface is scattered radially outward from the peripheral edge of the substrate by a centrifugal force generated by the rotation of the substrate. At this time, the splash guard is vertically moved to bring the first recovery port into opposed relation to a peripheral edge surface of the substrate, whereby the first process liquid scattered from the peripheral edge of the substrate is introduced into the first recovery port. Then, the first process liquid is recovered into the recovery tank through the recovery drain. Similarly, when a second process liquid is supplied to the substrate surface, the second recovery port is opposed to the peripheral edge surface of the substrate to recover the second process liquid scattered from the substrate. When a third process liquid is supplied to the substrate surface, the third recovery port is opposed to the peripheral edge surface of the substrate to recover the third process liquid scattered from the substrate.
Further, a rinsing operation is performed to rinse the substrate surface with pure water (process liquid) by supplying the pure water to the substrate surface while rotating the substrate by the spin chuck. At this time, the drain port is opposed to the peripheral edge surface of the substrate, whereby the pure water used for the rinsing of the substrate surface is collected in the drain channel and drained from the drain channel through the waste liquid drain.
However, the substrate processing apparatus having the aforesaid construction has several problems.
1. The recovery ports are constantly open. Therefore, even with a predetermined one of the recovery ports and the drain port being opposed to the peripheral edge surface of the substrate, the process liquid scattered from the substrate is liable to enter the other ports (particularly the ports adjacent to the predetermined one port), thereby contaminating the process liquids recovered through the other ports in the corresponding recovery channels. During the process with the first process liquid, for example, the scattered first process liquid is liable to partly enter the second recovery port even with the first recovery port being opposed to the peripheral edge surface of the substrate, thereby contaminating the second process liquid recovered in the second recovery channel. Further, with the first recovery port being opposed to the peripheral edge surface of the substrate, i.e., with the splash guard being located at the lowermost position, the lower edges of the respective guards are inserted in the drain channel and the recover channels to a greater extent, so that gaps between the lower edges of the respective guards and the cup are narrowed. Therefore, the process liquids in the recovery channels and the drain channel are liable to flow into the other channels by the capillary phenomenon.
2. When the lowermost drain port is brought into opposed relation to the peripheral edge surface of the substrate, the splash guard should be moved up a greater distance. Therefore, a greater space should be provided above the cup, so that the apparatus has a greater height.
3. Where types of process liquids to be recovered are increased, the existing cup should be replaced with a cup having a correspondingly increased number of recovery channels, and the existing splash guard should be replaced with a splash guard having a correspondingly increased number of guards. This inevitably results in a significant cost increase. In addition, the height of the splash guard is increased, thereby the vertical movement distance of the splash guard is further increased. This increases the height of the apparatus.
4. The recovery ports are constantly open. Therefore, when the splash guard is moved up or down for performing the rinsing operation immediately after the process with the first or second process liquid or performing the process with the first or second process liquid immediately after the rinsing operation, the process liquid scattered from the substrate is liable to enter a recovery port disposed between the first or second recovery port and the drain port during the upward or downward movement of the splash guard, thereby contaminating the process liquid to be recovered through that recovery port. When the splash guard is moved up for performing the rinsing operation immediately after the process with the second process liquid, for example, the third recovery port is brought into opposed relation to the peripheral edge surface of the substrate during the upward movement of the splash guard. At this time, the second process liquid scattered from the substrate is liable to enter the third recovery port, thereby contaminating the third process liquid to be recovered in the third recovery channel.
A conceivable approach to prevention of the contamination of the process liquids is to stop the rotation of the substrate by the spin chuck during the upward or downward movement of the splash guard. However, if the rotation of the substrate is once stopped, it takes time to increase the rotation speed of the substrate to a predetermined speed (a rotation speed required for the subsequent process), thereby prolonging the substrate process time. This reduces the process throughput. Therefore, the stop of the rotation of the substrate during the upward or downward movement of the splash guard is not a preferred approach to the prevention of the contamination of the process liquid.
5. The rinsing operation is performed after the processes with the first process liquid, the second process liquid and the third process liquid are each performed. Therefore, an atmosphere containing a mist of pure water used for washing away the process liquid used for the preceding process is produced during the rinsing operation. If such an atmosphere remains in the drain channel and around the substrate, the rinsed substrate may be adversely affected. Therefore, the atmosphere around the substrate is preferably sucked through the drain channel so as to be removed by an evacuation line connected to the drain channel for forced evacuation of the drain channel.
However, the drain channel atmospherically communicates with the respective recovery channels. Therefore, if the drain channel is forcibly evacuated, the recovery channels are indirectly evacuated, whereby air streams flowing from the recovery ports to the recovery channels occur. As a result, droplets of the process liquid to be drained into the drain channel enter the recovery channels from the recovery ports, thereby reducing the purities of the process liquids recovered in the respective recovery channels.